Dual clutch transmission

ABSTRACT

A transmission includes an input member, an output member, first and second shafts, first and second countershafts, a plurality of co-planar gear sets, and a plurality of torque transmitting devices. The torque transmitting devices include a plurality of synchronizer assemblies and a dual clutch assembly. The transmission is operable to provide at least one reverse speed ratio and a plurality of forward speed ratios between the input member and the output member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/165,997, filed on Apr. 2, 2009, which is hereby incorporated in itsentirety herein by reference.

TECHNICAL FIELD

The present disclosure relates to transmissions and more particularly toa compact, dual clutch transmission having three axes to establish sixgear speeds of which one could be a reverse gear speed.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may or may not constitute priorart.

A typical multiple speed transmission having countershafts and co-planargear sets uses countershaft gears with a different, dedicated gear pairor set to achieve each forward speed ratio. Accordingly, the totalnumber of gears required in this typical design is two times the numberof forward speeds, plus three for reverse. This necessitates a largenumber of required gear pairs, especially in transmissions that have arelatively large number of forward speed ratios.

While current transmissions achieve their intended purpose, the need fornew and improved transmission configurations which exhibit improvedperformance, especially from the standpoints of efficiency,responsiveness and smoothness and improved packaging, primarily reducedsize and weight, is essentially constant. Accordingly, there is a needin the art for a transmission having improved packaging while providingdesirable gear ratios and torque ranges.

SUMMARY

The present invention provides a transmission having an input member, anoutput member, first and second shaft members, first and secondcountershafts, a plurality of co-planar gear sets and a plurality oftorque transmitting devices. The torque transmitting devices include aplurality of synchronizer assemblies and a dual clutch assembly. Thetransmission is operable to provide at least one reverse speed ratio anda plurality of forward speed ratios between the input member and theoutput member.

In one aspect of the present invention, the transmission includes sixco-planar gear sets.

In yet another aspect of the present invention, the transmissionincludes four synchronizer assemblies.

In yet another aspect of the present invention, the four synchronizerassemblies includes two two-way synchronizers.

In yet another aspect of the present invention, the four synchronizerassemblies includes two one-way synchronizers.

In yet another aspect of the present invention, the transmission isoperable to provide at least five forward speed ratios.

In still another aspect of the present invention, a dual clutchtransmission having a transmission housing, six gear sets, a first andsecond transmission input member, a dual clutch assembly, a first andsecond countershaft and four synchronizer assemblies is provided.

In still another aspect of the present invention, the first gear setincludes a first gear in mesh with a third gear and a second gear inmesh with the third gear. The second gear set includes a first gear inmesh with a second gear and a third gear in mesh with the second gear.The third gear set includes a first gear in mesh with a second gear. Thefourth gear set includes a first gear in mesh with a second gear. Thefifth gear set includes a first gear in mesh with a second gear. Thesixth gear set includes a first gear in mesh with a second gear.

In still another aspect of the present invention, the first transmissioninput member is rotatably supported in the transmission housing. Each ofthe first gear of the fourth, fifth and sixth gear sets are rotatablyfixed for common rotation with the first transmission input member.

In still another aspect of the present invention, the secondtransmission input member is rotatably supported in the transmissionhousing. Each of the first gear of the first, second and third gear setsare rotatably fixed for common rotation with the second transmissioninput member. The second transmission input member is concentric withthe first transmission input member and at least partially surrounds thefirst transmission input member.

In still another aspect of the present invention, the dual clutchassembly has a clutch housing connectable to a flywheel of an engine, afirst clutch configured to selectively connect the clutch housing to thefirst transmission input member and a second clutch configured toselectively connect the clutch housing to the second transmission inputmember. The clutch housing is rotationally supported within thetransmission housing.

In still another aspect of the present invention, the first countershaftis rotatably supported within the transmission housing and spaced apartfrom and parallel with the first and second transmission input members.The second gear of the fourth gear set, the fifth gear set and the sixthgear set are each selectively connectable for common rotation with thefirst countershaft and the third gear of the first gear set is supportedon and rotatable about the first countershaft.

In still another aspect of the present invention, the secondcountershaft is rotatably supported within the transmission housing andspaced apart from and parallel with the first and second transmissioninput members. The second gear of the first gear set, the second gearset and the third gear set are each selectively connectable for commonrotation with the second countershaft.

In still another aspect of the present invention, the first synchronizerassembly is configured to selectively connect the second gear of thefirst gear set to the second countershaft shaft to establish a reversegear ratio when the second clutch of the dual clutch assembly is engagedto connect the clutch housing of the dual clutch to the secondtransmission input member.

In still another aspect of the present invention, the secondsynchronizer is configured to selectively connect the second gear of thesecond gear set to the second countershaft to establish a second gearratio and the second gear of the third gear set to the secondcountershaft to establish a fourth gear ratio when the second clutch ofthe dual clutch assembly is engaged to connect the clutch housing of thedual clutch to the second transmission input member;

In still another aspect of the present invention, the third synchronizerassembly is configured to selectively connect the second gear of thefourth gear set to the first countershaft to establish a fifth gearratio when the first clutch of the dual clutch assembly is engaged toconnect the clutch housing of the dual clutch to the first transmissioninput member.

In still another aspect of the present invention, the fourthsynchronizer assembly is configured to selectively connect the secondgear of the fifth gear set to the first countershaft to establish athird gear ratio and the second gear of the sixth gear set to the firstcountershaft to establish a first gear ratio when the first clutch ofthe dual clutch assembly is engaged to connect the clutch housing of thedual clutch to the first transmission input member.

The above features and advantages and other features and advantages ofthe present invention are readily apparent from the following detaileddescription of the best modes for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic diagram of an embodiment of a five speedtransmission, in accordance with the present invention; and

FIG. 2 is a schematic diagram of an embodiment of a five speedtransmission illustrating synchronizer locations, in accordance with thepresent invention.

DESCRIPTION

Referring to FIG. 1, a multiple speed transmission is generallyindicated by reference number 10. The transmission 10 is connectable toan input member 12 and includes a gearing arrangement 20. The gearingarrangement 20 includes various shafts or members, co-planarintermeshing gear sets, a dual clutch assembly, and selectivelyengageable synchronizers, as will be described herein. For example, thegearing arrangement 20 includes a first transmission input shaft ormember 22, a second transmission input shaft or member 24, a firstcountershaft 28 and a second countershaft 30. The second transmissioninput shaft or member 24 is a sleeve shaft that is concentric with andoverlies the first transmission input shaft or member 22. The first andsecond countershafts 28, 30 are spaced apart from and parallel with thefirst and second transmission input shaft members 22, 24. Moreover, thefirst and second countershafts 28, 30 are connectable through additionalgears and/or shafts (not shown) to a final drive assembly (not shown)that is configured to drive a pair of road wheels (not shown). The firstand second transmission input shafts 22, 24 define a first axis ofrotation, the first countershaft 28 defines a second axis of rotationand the second countershaft 30 defines a third axis of rotation.

A dual clutch assembly 32 is connected between the input member 12 andthe first and second transmission input shaft or members 22, 24. Thedual clutch assembly 32 includes a clutch housing 34 connectable to theinput member 12 for common rotation with the input member 12. The dualclutch assembly 32 could be either a dry or a wet clutch assembly.Further, the dual clutch assembly 32 has first and second clutchelements or hubs 36 and 38. Clutch elements 36 and 38 together with theclutch housing 34 are configured to form a friction clutch, as is knownin the art as a dual clutch. More specifically, clutch elements 36, 38and the clutch housing 34 have friction plates mounted thereon orotherwise coupled thereto that interact to form a friction clutch. Theclutch element 36 is connected for common rotation with the firsttransmission input shaft or member 22 and the clutch element 38 isconnected for common rotation with the second transmission input shaftor member 24. Thus, selective engagement of clutch element 36 with theclutch housing 34 connects the input member 12 for common rotation withthe first transmission input shaft member 22. Selective engagement ofclutch element 38 with the clutch housing 34 connects the input member12 for common rotation with the second transmission input shaft member24.

The gearing arrangement 20 also includes a plurality of co-planar,intermeshing gear sets 40, 50, 60, 70, 80 and 90. Co-planar gear sets40, 50, 60, 70, 80 and 90 include intermeshing gear pairs: gear 42 andgear 44, gear 52 and gear 54, gear 62 and gear 64, gear 72 and gear 74,gear 82 and gear 84 and gear 92 and gear 94, respectively. In anembodiment of the present invention, gears 42, 52, 62 are eitherrotatably fixed for common rotation with the second transmission inputshaft member 24 or are selectively connectable for common rotation withthe second transmission input shaft member 24. Gears 72, 82, 92 areeither rotatably fixed for common rotation with the first transmissioninput shaft member 22 or are selectively connectable for common rotationwith the first transmission input member 22. Gears 44, 54 and 64 areeither rotatably fixed for common rotation with the second countershaft30 or are selectively connectable for common rotation with the secondcountershaft 30. Further, gears 74, 84 and 94 are either rotatably fixedfor common rotation with the first countershaft 28 or are selectivelyconnectable for common rotation with the first countershaft 28. Theindividual gears of co-planar gear sets 40, 50, 60, 70, 80 and 90 areindependently and selectively connectable for common rotation with thefirst transmission input shaft 22, second transmission input shaftmember 24, first countershaft 28 or second countershaft 30 bysynchronizer assemblies, as will be further described hereinafter. Ofcourse, the present invention contemplates other selectively actuatabledevices other than synchronizers for connecting gears to shafts.

Referring now to FIG. 2, another embodiment of a multiple speedtransmission is generally indicated by reference number 100. Thetransmission 100 is connectable to an input shaft or member 112 andincludes an output gear or member 114. The input member 112 iscontinuously connected with an engine (not shown) or other torqueproducing machine to provide a driving torque to input member 112. Theoutput member 114 rotatably drives a final drive assembly 116. Morespecifically, the final drive assembly 116 includes a differential gearset coupled to and supported in a differential housing 117. Differentialhousing 117 is coupled to and is rotatably driven by output member 114.Further, differential housing 117 transfers torque delivered by outputmember 114 to the differential gear set that is rotatably coupled tofirst and second side axles 118, 119, and on to road wheels (not shown)coupled to side axles 118, 119.

The transmission 100 includes a housing 120 that at least partiallyencloses a gearing arrangement 122. As in the embodiment describedabove, the gearing arrangement 122 of transmission 100 includes a firsttransmission input shaft or member 124, a second transmission inputshaft or member 126, a first countershaft 128 and a second countershaft130. The second transmission input shaft or member 126 is a sleeve shaftthat is concentric with and overlies the first transmission input shaftor member 124. The first and second countershafts 128, 130 are eachspaced apart from and parallel with the first and second transmissioninput shaft or members 124,126. The first and second shafts 124,126define a first axis of rotation, the first countershaft 128 defines asecond axis of rotation and the second countershaft 130 defines a thirdaxis of rotation.

A dual clutch assembly 132 is connectable between the input member 112and the first and second transmission input shaft members 124, 126. Thedual clutch assembly 132 includes a clutch housing 134 connectable tothe input member 112 for common rotation with the input member 112.Further, the dual clutch assembly 132 has first and second clutchelements or hubs 136 and 138. Clutch elements 136 and 138 together withthe clutch housing 134 are configured to form a friction clutch, as isknown in the art as a dual clutch. More specifically, clutch elements136, 138 and the clutch housing 134 have friction plates mounted thereonor otherwise coupled thereto that interact to form a friction clutch.The clutch element 136 is connected for common rotation with the firsttransmission input shaft or member 124 and the clutch element 138 isconnected for common rotation with the second transmission input shaftor member 126. Thus, selective engagement of clutch element 136 with theclutch housing 134 connects the input member 112 for common rotationwith the first shaft member 124. Selective engagement of clutch element138 with the clutch housing 134 connects the input member 112 for commonrotation with the second transmission input shaft member 126.

The gearing arrangement 122 also includes a plurality of co-planar,intermeshing gear sets 140, 150, 160, 170, 180 and 190. Co-planar gearset 140 includes gear 142, gear 144 and gear 146. Gear 142 is rotatablyfixed and connected for common rotation with the second shaft 126. Gear144 is selectively connectable for common rotation with the secondcountershaft member 130 and intermeshes with gear 146. Gear 146 issupported by and free to rotate on and independent of the firstcountershaft 128 and intermeshes with gear 142 and gear 144. It shouldbe appreciated that gear 142 may be a separate gear structure fixed tothe second shaft member 126 or gear teeth/splines formed on an outersurface of the second shaft member 126 without departing from the scopeof the present invention. Gear set 140 is disposed adjacent a wall 148of the transmission housing 120 that is on a front or side of thetransmission 100 proximate the dual clutch assembly 132.

Co-planar gear set 150 includes gear 152 and gear 154. Gear 152 isrotatably fixed and connected for common rotation with the second shaftmember 126 and intermeshes with gear 154. Gear 154 is selectivelyconnectable for common rotation with the second countershaft 130. Gearset 150 is positioned adjacent gear set 140.

Co-planar gear set 160 includes gear 162 and gear 164. Gear 162 isrotatably fixed and connected for common rotation with the second shaftmember 126 and intermeshes with gear 164. Gear 164 is selectivelyconnectable for common rotation with the second countershaft 130. Gearset 160 is disposed adjacent gear set 150.

Co-planar gear set 170 includes gear 172 and gear 174. Gear 172 isrotatably fixed and connected for common rotation with the first shaft124 and intermeshes with gear 174. Gear 174 is selectively connectablefor common rotation with the first countershaft member 128. Gear set 170is located adjacent gear set 160.

Co-planar gear set 180 includes gear 182 and gear 184. Gear 182 isrotatably fixed and connected for common rotation with the first shaftmember 124 and intermeshes with gear 184. Gear 184 is selectivelyconnectable for common rotation with the first countershaft 128. Gearset 180 is positioned adjacent gear set 170.

Co-planar gear set 190 includes gear 192 and gear 194. Gear 192 isrotatably fixed and connected for common rotation with the first shaftmember 124 and intermeshes with gear 194. Gear 194 is selectivelyconnectable for common rotation with the first countershaft 128. Gearset 190 is positioned between gear set 180 and an end wall 200 oftransmission 100.

It should be noted that gear sets 140, 150, 160, 170, 180 and 190 can berearranged in sequence and not deviate from the intent of the invention.

Further, a first countershaft transfer gear 202 is rotatably fixed andconnected for common rotation with the first countershaft member 128. Asecond countershaft transfer gear 204 is rotatably fixed and connectedfor common rotation with the second countershaft member 130. Firstcountershaft transfer gear 202 is configured to mesh with output member114 and the second countershaft transfer gear 204 is configured to meshwith output member 114. However, the first countershaft transfer gear202 and the second countershaft transfer gear 204 do not mesh with eachother. The first countershaft transfer gear 202 is disposed between gear146 and end wall 148 of the transmission housing 120. The secondcountershaft transfer gear 204 is disposed between gear 144 and end wall148 of the transmission housing 120. The output member 114 is co-planarwith first and second countershaft transfer gears 202, 204 andpositioned between the gear set 140 and end wall 148 of the transmissionhousing 120.

The transmission 100 further includes a plurality of selectivelyactuatable synchronizer assemblies 210, 212, 214 and 216. Synchronizers210 and 214 are single sided synchronizers that generally include ashift fork (not shown) that is bi-directionally translated by anactuator (not shown) into either an engaged position or a neutral ordisengaged position. In the present embodiment, synchronizer 210 isselectively actuatable to connect gear 144 for common rotation with thesecond countershaft 130 and synchronizer 214 is selectively actuatableto connect gear 174 for common rotation with the first countershaftmember 128. In a preferred embodiment, synchronizers 210, 214 have onlyone actuator.

Synchronizers 212 and 216 are double sided synchronizers and generallyinclude a shift fork (not shown) that is bi-directionally translated byan actuator (not shown) into at least two engaged positions and aneutral or disengaged position. In the present embodiment, synchronizer212 is selectively actuatable to connect for common rotation gear 154with the second countershaft 130 and is selectively actuatable toconnect for common rotation gear 164 with the second countershaft 130.Synchronizer 216 is selectively engageable to connect for commonrotation gear 184 with the first countershaft 128 and is selectivelyengageable to connect for common rotation gear 194 with the firstcountershaft 128.

The transmission 100 is capable of transmitting torque from the inputshaft 112 to the output member 114 in at least five forward torqueratios and at least one reverse torque ratio. Each of the forward torqueratios and the reverse torque ratio is attained by selective engagementof the dual clutch assembly 132 and one or more of the synchronizerassemblies 210, 212, 214 and 216. Those skilled in the art will readilyunderstand that a different speed ratio is associated with each torqueratio.

It should be appreciated that each individual gear set 140, 150, 160,170, 180 and 190 provides one or more forward and/or reverse gear ratiosupon selective engagement of the synchronizer assemblies 210, 212, 214and 216. However, which synchronizer and which gear set are associatedwith a particular forward or reverse speed ratio may vary withoutdeparting from the scope of the present invention.

For example, to establish the reverse torque ratio, clutch element 138is engaged to couple the input member 112 with the second shaft 126 andsynchronizer 210 is engaged to connect gear 144 to the secondcountershaft 130. More specifically, input torque from the input shaft112 is transferred through the dual clutch assembly 132 to the secondshaft 126, through gear 142 to gear 146, through gear 146 to gear 144,from gear 144 to synchronizer 210, from synchronizer 210 to secondcountershaft 130, from second countershaft 130 to transfer gear 204,from transfer gear 204 to output gear 114 and from output gear 114 todifferential housing 117 of final drive assembly 116.

To establish a first forward torque ratio (i.e. a 1st gear), clutchelement 136 is engaged to couple the input member 112 with the firstshaft member 124 and synchronizer 216 is activated to couple gear 194 tothe first countershaft 128. Input torque from the input member 112 istransferred through the dual clutch assembly 132 to the first shaftmember 124 to gear 192. Gear 192 transfers torque to gear 194 whichtransfers the torque to the first countershaft 128 through synchronizer216 and from the first countershaft 128 to transfer gear 202 and fromtransfer gear 202 to output gear 114 and from output gear 114 todifferential housing 117 of final drive assembly 116.

To establish a second forward torque ratio (i.e. a 2nd gear), clutchelement 138 is engaged to couple the input member 112 to the secondshaft 126 which rotates gear 152 and synchronizer 212 is activated tocouple gear 154 to the second countershaft member 130. Accordingly,input torque from the input member 112 is transferred through the dualclutch assembly 132 to the second shaft member 126 to gear 152. Gear 152transfers torque to gear 154 which transfers the torque to the secondcountershaft 130 through synchronizer 212 and from the secondcountershaft 130 to transfer gear 204 and from transfer gear 204 tooutput gear 114 and from output gear 114 to differential housing 117 offinal drive assembly 116.

To establish a third forward torque ratio (i.e. a 3rd gear), clutchelement 136 is engaged to couple the input member 112 to the first shaft124 which rotates gear 182 and synchronizer 216 is engaged to couplegear 184 to the first countershaft 128. Accordingly, input torque fromthe input member 112 is transferred through the dual clutch assembly 132to the first shaft 124 to gear 182. Gear 182 transfers torque to gear184 which transfers the torque to the first countershaft 128 throughsynchronizer 216 and from the first countershaft 128 to transfer gear202 and from transfer gear 202 to output gear 114 and from output gear114 to differential housing 117 of final drive assembly 116.

To establish a fourth forward torque ratio (i.e. a 4th gear), clutchelement 138 is engaged to couple the input member 112 to the secondshaft member 126 which rotates gear 162 and synchronizer 212 isactivated to couple gear 164 to the second countershaft 130. Thus, inputtorque from the input member 112 is transferred through the dual clutchassembly 132 to the second shaft 126 to gear 162. Gear 162 transferstorque to gear 164 which transfers the torque to the second countershaft130 through synchronizer 212 and from the second countershaft 130 totransfer gear 204 and from transfer gear 204 to output gear 114 and fromoutput gear 114 to differential housing 117 of final drive assembly 116.

To establish a fifth forward torque ratio (i.e. a 5th gear), clutchelement 136 is engaged to couple the input member 112 to the first shaft124 which rotates gear 172 and synchronizer 214 is activated to couplegear 174 to the first countershaft 128. Thus, input torque from theinput member 112 is transferred through the dual clutch assembly 132 tothe first shaft 124 to gear 172. Gear 172 transfers torque to gear 174which transfers the torque to the first countershaft 128 throughsynchronizer 214 and from the first countershaft 128 to transfer gear202 and from transfer gear 202 to output gear 114 and from output gear114 to differential housing 117 of final drive assembly 116.

Again, it should be appreciated that any one of the gear sets of gearsets 140, 150, 160, 170, 180 and 190 may be interchanged to produce acertain forward and reverse torque ratio without departing from thescope of the present invention.

The present invention contemplates that a variety of torque ratios(i.e., the ratio of torque of the output member 114 to the input member112) are achievable through the selection of tooth counts of the gearsof the transmission 100. This arrangement provides the opportunity toachieve reduced transmission length in comparison with othertransmissions.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

1. A transmission comprising: a transmission housing; a dual clutchassembly having a clutch housing connectable to a flywheel of an engine,wherein the clutch housing is rotationally supported within thetransmission housing; a first, second, third, fourth, fifth and sixthgear sets, wherein the first gear set includes a first gear in mesh witha third gear and a second gear in mesh with the third gear, the secondgear set includes a first gear in mesh with a second gear and a thirdgear in mesh with the second gear, the third gear set includes a firstgear in mesh with a second gear, the fourth gear set includes a firstgear in mesh with a second gear, the fifth gear set includes a firstgear in mesh with a second gear and the sixth gear set includes a firstgear in mesh with a second gear; a first transmission input memberrotatably supported in the transmission housing and wherein each of thefirst gear of the fourth, fifth and sixth gear sets are rotatably fixedfor common rotation with the first transmission input member; a secondtransmission input member rotatably supported in the transmissionhousing, wherein each of the first gear of the first, second and thirdgear sets are rotatably fixed for common rotation with the secondtransmission input member and wherein the second transmission inputmember is concentric with the first transmission input member and atleast partially surrounds the first transmission input member; a firstcountershaft rotatably supported within the transmission housing andspaced apart from and parallel with the first and second transmissioninput members, wherein the second gear of the fourth gear set, the fifthgear set and the sixth gear set are each selectively connectable forcommon rotation with the first countershaft and the third gear of thefirst gear set is supported on and rotatable about the firstcountershaft; a second countershaft rotatably supported within thetransmission housing and spaced apart from and parallel with the firstand second transmission input members, wherein the second gear of thefirst gear set, the second gear set and the third gear set are eachselectively connectable for common rotation with the secondcountershaft; four synchronizer assemblies for selectively coupling atleast one of the gears of the first, second, third, fourth, fifth andsixth gear sets with at least one of the first countershaft and thesecond countershaft, and wherein the selective engagement of dual clutchassembly interconnects the dual clutch housing with at least one of thefirst and the second transmission input members and the selectiveengagement of at least one of the four synchronizer assembliesestablishes at least one of five forward speed ratios.
 2. Thetransmission of claim 1 wherein a first of the four synchronizerassemblies selectively connects the second gear of the first gear set tothe second countershaft shaft.
 3. The transmission of claim 2 wherein asecond of the four synchronizer assemblies selectively connects at leastone of the second gear of the second gear set and second gear of thethird gear set to the second countershaft shaft.
 4. The transmission ofclaim 3 wherein a third of the four synchronizer assemblies selectivelyconnects the second gear of the fourth gear set to the firstcountershaft shaft.
 5. The transmission of claim 4 wherein a fourth ofthe four synchronizer assemblies selectively connects at least one ofthe second gear of the fifth gear set and the second gear of the sixthgear set to the first countershaft shaft.
 6. The transmission of claim 1wherein the first gear set is adjacent the dual clutch assembly, thesecond gear set is adjacent the first gear set, the third gear set isadjacent the second gear set, the fourth gear set is adjacent the thirdgear set, the fifth gear set is adjacent the fourth gear set and thesixth gear set is between an end wall of the transmission housing andthe fifth gear set.
 7. The transmission of claim 1 wherein the dualclutch assembly includes a first clutch and a second clutch, wherein thesecond clutch is configured to selectively connect the clutch housing tothe second transmission input member and wherein the four synchronizerassemblies includes a first synchronizer assembly for selectivelyconnecting the second gear of the first gear set to the secondcountershaft to establish a reverse gear ratio.
 8. The transmission ofclaim 7 wherein the second clutch of the dual clutch assembly isconfigured to selectively connect the clutch housing to the secondtransmission input member and wherein the second synchronizer of thefour synchronizer assemblies is configured to selectively connect thesecond gear of the second gear set to the second countershaft toestablish a second gear ratio.
 9. The transmission of claim 8 whereinthe second clutch of the dual clutch assembly is configured toselectively connect the clutch housing to the second transmission inputmember and wherein the second synchronizer assembly of the foursynchronizer assemblies is configured to selectively connect the secondgear of the third gear set to the second countershaft to establish afourth gear ratio.
 10. The transmission of claim 9 wherein the firstclutch of the dual clutch is configured to selectively connect theclutch housing to the first transmission input member and wherein athird synchronizer assembly of the four synchronizer assemblies isconfigured to selectively connect the second gear of the fourth gear setto the first countershaft to establish a fifth gear ratio.
 11. Thetransmission of claim 10 wherein the first clutch of the dual clutch isconfigured to selectively connect the clutch housing to the firsttransmission input member and wherein the fourth synchronizer assemblyof the four synchronizer assemblies is configured to selectively connectthe second gear of the fifth gear set to the first countershaft toestablish a third gear ratio.
 12. The transmission of claim 11 whereinthe first clutch of the dual clutch is configured to selectively connectthe clutch housing to the first transmission input member and whereinthe fourth synchronizer assembly of the four synchronizer assemblies isconfigured to selectively connect the second gear of the sixth gear setto the first countershaft to establish a first gear ratio.
 13. Thetransmission of claim 1 further comprising a first countershaft transfergear fixed to the first countershaft for common rotation with the firstcountershaft and a second countershaft transfer gear fixed to the secondcountershaft for common rotation with the second countershaft andwherein the first and second countershaft transfer gears transfer torquefrom at least one of the first and second countershafts to an outputmember.
 14. The transmission of claim 13 wherein the output member is agear that meshes with the each of the first and second countershafttransfer gears.
 15. A dual clutch transmission comprising: atransmission housing; a first, second, third, fourth, fifth and sixthgear sets, wherein the first gear set includes a first gear in mesh witha third gear and a second gear in mesh with the third gear, the secondgear set includes a first gear in mesh with a second gear and a thirdgear in mesh with the second gear, the third gear set includes a firstgear in mesh with a second gear, the fourth gear set includes a firstgear in mesh with a second gear, the fifth gear set includes a firstgear in mesh with a second gear and the sixth gear set includes a firstgear in mesh with a second gear; a first transmission input memberrotatably supported in the transmission housing and wherein each of thefirst gear of the fourth, fifth and sixth gear sets are rotatably fixedfor common rotation with the first transmission input member; a secondtransmission input member rotatably supported in the transmissionhousing, wherein each of the first gear of the first, second and thirdgear sets are rotatably fixed for common rotation with the secondtransmission input member and wherein the second transmission inputmember is concentric with the first transmission input member and atleast partially surrounds the first transmission input member; a dualclutch assembly having a clutch housing connectable to a flywheel of anengine, a first clutch configured to selectively connect the clutchhousing to the first transmission input member and a second clutchconfigured to selectively connect the clutch housing to the secondtransmission input member and wherein the clutch housing is rotationallysupported within the transmission housing; a first countershaftrotatably supported within the transmission housing and spaced apartfrom and parallel with the first and second transmission input members,wherein the second gear of the fourth gear set, the fifth gear set andthe sixth gear set are each selectively connectable for common rotationwith the first countershaft and the third gear of the first gear set issupported on and rotatable about the first countershaft; a secondcountershaft rotatably supported within the transmission housing andspaced apart from and parallel with the first and second transmissioninput members, wherein the second gear of the first gear set, the secondgear set and the third gear set are each selectively connectable forcommon rotation with the second countershaft; a first synchronizerassembly configured to selectively connect the second gear of the firstgear set to the second countershaft shaft to establish a reverse gearratio when the second clutch of the dual clutch assembly is engaged toconnect the clutch housing of the dual clutch to the second transmissioninput member; a second synchronizer configured to selectively connectthe second gear of the second gear set to the second countershaft toestablish a second gear ratio and the second gear of the third gear setto the second countershaft to establish a fourth gear ratio when thesecond clutch of the dual clutch assembly is engaged to connect theclutch housing of the dual clutch to the second transmission inputmember; a third synchronizer assembly configured to selectively connectthe second gear of the fourth gear set to the first countershaft toestablish a fifth gear ratio when the first clutch of the dual clutchassembly is engaged to connect the clutch housing of the dual clutch tothe first transmission input member; and a fourth synchronizer assemblyconfigured to selectively connect the second gear of the fifth gear setto the first countershaft to establish a third gear ratio and the secondgear of the sixth gear set to the first countershaft to establish afirst gear ratio when the first clutch of the dual clutch assembly isengaged to connect the clutch housing of the dual clutch to the firsttransmission input member.